Electrically-heatable hoses for use in motor vehicles are known in many forms. The medium which flows between two connecting points in these hoses is heated by these hoses.
A heatable hose with at least one electrical heating conductor, which is used to heat a medium flowing in the hose, is known, for example, from German patent publication 102 01 920 A1, where the heating conductor extends over at least part of the length of the hose and is comprised of a metallic core and a jacket.
The heating conductor is usually embedded in a layer of the hose. In a multi-layer hose, the heating conductor, can also he arranged between two layers. The ends of the heating conductor are exposed in order to be able to connect them to a voltage source which is necessary to operate the heating conductor. The exposed ends of the heating conductor are usually arranged at one end of the hose. However, it is also possible for an exposed end of the heating conductor to be arranged at each end of the hose.
The exposed ends of the heating conductor are provided with an electrical connection (plug) and are then connected to a voltage source. Since the voltage source is usually not arranged directly on the hose, the exposed ends of the heating conductor must be of a predefined length in order to be able to connect them to the voltage source via the plug.
European patent publication 1 329 660 B1 discloses a flexible multi-layer heatable hose having at least one reinforcement layer and an elastomer outer layer as well as an electrical heating conductor which is used to heat a medium flowing in the hose. The heating conductor extends over at least part of the length of the hose and is comprised of a metallic core and a jacket. The heating conductor is embedded outside the outer stratum of the reinforcement layer but under or inside the elastomer outer layer. In order to permit a simple and reliable electrical contact to be made between the heating conductor and a voltage source, the elastomer outer layer has a lesser strength than the heating conductor. This strength is dimensioned in such a way that the heating conductor can be exposed by means of a radially outwardly acting force by cutting through the original or weakened elastomer outer layer, but without damaging its metallic core and its jacket, and can be connected directly to an electrical connection. The heating conductor preferably extends in a helical shape at least over part of the length of the hose under or inside the elastomer outer layer.
Because the heating conductor is arranged outside the outer stratum of the reinforcement layer but under or inside the elastomer outer layer it is possible to expose the heating conductor without intervening in the reinforcement layer. This process can be carried out in the simplest case with pincers, with which the ends of the heating conductor, which are freely accessible at the front end of a hose section, are grasped and pulled radially outward. By preserving the jacket, the electrical insulation is maintained so that the metallic core cannot be adversely affected by corrosion or short-circuiting owing to penetrating moisture. The function of the elastomer outer layer is also maintained because the elastomer outer layer is cut only in the direct area in which the heating conductor is pulled radially outward. In the remaining area, the elastomer outer layer remains entirely unaffected. The heating conductor can therefore be led directly, that is, without additional insulation, to an electrical connection and connected electrically there.
It is disadvantageous that the exposed ends of the heating conductor, which are of a predefined length, are virtually completely unprotected from the point where they emerge from the hose up to their connecting point.
In order to ensure that the exposed ends of the heating conductor are protected over a predefined length from the point where they emerge from the hose up to their connection to an electrical component (for example, a voltage source), European patent publication 1 610 049 A2 discloses plugging a tube segment onto the end of the hose. The surface of the tube segment is connected to a tubular stub, which is arranged at an angle with respect to the longitudinal axis of the tube segment and in which connector element the exposed ends of the heating conductor are guided, the lateral surface having a passage leading to the connector element here.
This embodiment ensures, in the mounted state of the hose connecting system, that the ends of the heating conductor which are exposed over a predefined length at the end of the hose are not exposed immediately after the point where they emerge from the hose as far as their connection to an electrical component but are instead guided in a protected fashion in the connector element which is connected to the tubular element. In the mounted state, the connector element is preferably embodied in the manner of a 45° or 90° angular element. As a result, the ends of the heating conductor can be led to an electrical component which is arranged above the hose.
The described technology of the heatable hoses has been proven in the transportation of fluid media between two connecting points or connector elements for motor vehicle assemblies such as, for example, a reservoir tank, injection unit, pump etc. However, in particular applications it has been found that the fluid medium can freeze in the hose connector elements of the connecting blocks, which are usually embodied as standardized plug-in connectors, in particular quick-action plug-in connectors, and arranged at the hose ends.
This risk of freezing occurs, in particular, in exhaust gas post-treatment systems for reducing nitrogen oxide emissions of an internal combustion engine. In this context, nitrogen oxide is converted into atmospheric nitrogen and water vapor using selective catalytic reduction (SCR) technology. The reducing agent used here is aqueous urea solution which is carried along in the motor vehicle in a separate reservoir container. The aqueous urea solution is fed out of the reservoir container by a feed module or a pump and fed to a metering module, from which the urea solution is injected in a metered fashion into the exhaust gas stream upstream of the catalytic converter. Excess reducing agent is fed back into the reservoir container by the feed module via a return line.
Hose lines for conveying the reducing agent are present between the reservoir container, the feed module and the metering module. These hose lines have to be connected to the specified assemblies in order to produce the fluid connection.
For the hose connections to the assemblies, it is possible to use the quick-action plug-in connectors standardized in the automobile industry, at those hose ends whose receptacle part is mounted on the assemblies ex-factory. The quick-action plug-in connectors (quick connectors) have the advantage of rapid mounting of the hose and are known in a variety of embodiments. They are most frequently embodied as a “male part” on the assemblies and as a “female part” on the hose ends, the latter having a connector element for the hose end, onto which the end of the hose to be connected is pushed in a media-tight fashion and fastened.
The hose lines between the reservoir container and the exhaust gas line have to be capable of being heated, since below −11° C. there is a risk of the aqueous urea solution freezing. It is known to avert the risk of freezing by using the known, electrically heatable hoses. Although these electrically heatable hoses have been proven, in extreme applications the plug-in connectors are the weak point of the exhaust gas treatment systems in terms of the risk of freezing. There is still a risk of freezing in the plug-in connectors themselves.
In order to provide a device which provides protection against freezing of the aqueous urea solution even in the connections of the hose lines to the assemblies to be connected, it would be possible to use, for the hose connections, connecting blocks which can be heated by cooling water and which are embodied in such a way that the cooling water whose temperature can be controlled is rinsed through them. As a result, not only the hoses but also the plug-in connectors could be thawed.
The use of special quick-action plug-in connectors (quick connectors) which have a separate electrical heating element (for example a heatable ceramic component) would also be conceivable. It is disadvantageous that this is a very expensive and complex solution which also requires an additional electrical connection (plug).